1. Field of the Invention
The present invention relates to an all terrain vehicle having a structure for adjusting the tension of the drive chain using an eccentric hub that rotatably supports the rear axle in a position eccentric to the center of the axle supporting section, and the method of adjusting the tension thereof.
2. Description of the Related Art
Hitherto, so-called all terrain vehicles (ATVs) have been provided which can travel on any terrain such as bog, sandy beaches, snowy roads, and mountain paths. All terrain vehicles generally have two rear wheels, that is, a right rear wheel and a left rear wheel. The right rear wheel and the left rear wheel are connected to a rear axle. The rear axle is rotatably supported by the axle supporting section of the rear arm and rotated by a driven sprocket around which a drive chain is wound.
For such all terrain vehicles, a structure is known in which the tension of the drive chain is adjusted by an eccentric hub, a so-called eccentric mechanism, that supports the rear axle rotatably in a position eccentric to the center of the axle supporting section (for example, JP-A-2000-108975, pp. 3-4, FIG. 4).
Specifically, the rear axle is passed through an eccentric hub that off-centers the rear axle from the center of the axle supporting section. When the all terrain vehicle is moved rearward, after a tightening bolt at the axle supporting section has been loosened, the rear axle is moved rearward owing to the shape of the eccentric hub. When the rear axle is moved rearward, the driven sprocket is separated from a drive sprocket disposed ahead of the driven sprocket to increase the tension of the drive chain. Then the tightening bolt at the axle supporting section is tightened at a position where an appropriate tension of the drive chain is given, so that the adjustment of the tension of the drive chain is completed.
However, such a related-art drive-chain adjusting structure has the following problem: if an all terrain vehicle is excessively moved backward during adjustment of the tension of the drive chain, the tension is loosened.
Specifically, if an all terrain vehicle is excessively moved backward, the rear axle is moved forward from a position most eccentric to the center of the axle supporting section, that is, from the position nearest the back. That is, the tension of the drive chain is loosened as the driven sprocket approaches the drive sprocket.